Possible to get the data individually from different data sources and combine it with spreadsheet functions

If you were already using Sheets before, then the biggest advantage is using the connectors in Data Studio to connect directly to those data sources and refresh in real-time, and being able to change queries on the fly in Data Studio without having the extra step of manipulating the sheet data first.

The biggest downside is that if you need to do any data manipulation or merge sources, then Data Studio is very poor at this.

We do have a special connector in Data Studio called "Ad Data + Google Analytics" that lets you blend cost and campaign data into a single report element from multiple sources, which helps get around the usual limitation that you can't combine multiple sources into 1 element. But it's also very focused on CPC and campaign overview so it doesn't have the full set of fields that the separate connectors has.

It is not subject to the 2mil cell limit (as it doesn't have cells per se), but there is a functional limitations in Data Studio that make it so that queries that take more than 6 minutes aren't handled. So large data sets are still problematic, just in a different way.

I hope this helps. Please let us know if you have any other questions about this.